Greek Prime Minister Alexis Tsipras is facing a showdown both with international creditors and dissenters in his party as his government toils to reach a default-saving loan deal in less than a month.
Athens this week opted to bundle four IMF loan payments into a single one due by the end of June, giving the 40-year-old premier just weeks to reach an agreement with creditors that sceptics in his hard-left party could accept.
Greece and its international creditors have wrangled for weeks as they try to hammer out a reform plan that would unlock the final 7.2 billion euros ($8 billion) in bailout funds for Athens.
Late on Friday Tsipras rebuffed creditor proposals as "absurd" in a bid to galvanise support at home, but it was unclear whether the message has won over the hardliners in his radical Syriza party.
The outburst was coldly received in some European circles, with one source saying it was tantamount to Tsipras "spitting in the soup."
"There is a feeling of fatigue and disappointment among the creditors," the European source told AFP, noting that the Greek PM's tone was "very aggressive".
Athens this week withheld a 300-million-euro loan repayment to the International Monetary Fund, opting instead to group four scheduled tranches into a single payment at the end of the month.
This means that Greece must now find 1.6 billion euros in three weeks -- funds it is unlikely to muster without a deal with its EU-IMF creditors.
This, in turn, is unlikely given the creditor demands, said Greek Energy Minister Panagiotis Lafazanis, the ruling party's top EU sceptic.
"It is obvious that given their demands, there can be no convergence between our government and the institutions," Lafazanis, who is believed to influence a third of the party, told The Telegraph.
"The ball is now in their court," government spokesman Gabriel Sakellaridis wrote in Efimerida ton Syntakton daily.
"We will insist on dialogue, but we will not accept ultimata," he said.
Many within Syriza, including a number of cabinet members, say the PM should even call early elections rather than accept further austerity measures.
- 'The bell will toll for many' -
In a speech to parliament late on Friday Tsipras called for cross-party support for his government.
"It is clear that the Greek government cannot under any circumstances consent to absurd proposals," he said.
Greece's lenders have insisted on higher primary budget surplus targets than Athens would like, financed by increased rates of sales tax, cuts in civil servants' salaries and pensions.
In contrast, Athens insists on a new restructuring of the country's massive debt, arguing that it is the only means to ensure the Greek economy's long-term recovery.
The International Monetary Fund supports this position but many eurozone countries including Germany vehemently oppose such a move, pointing to a drastic debt write-down granted to Greece in 2012.
Poking fun at the arduous Greek talks, German tabloid Bild on Saturday portrayed Tsipras and his Finance Minister Yanis Varoufakis as bearded old men seated outside a cafe.
The Greeks have a "nutty 100-year plan" to repay the country's debt, the tabloid jeered.
Tsipras on Friday argued that a "cynical" policy of economic asphyxiation and harsh austerity being applied to Greece will ultimately impact other European states in economic difficulty.
"Those who believe that a punishment of Greece will only strike Greece are deeply in the dark," Tsipras said.
"The bell will toll mainly for the countries in southern Europe" that currently benefit from ECB stimulus policies, he said.
Should Greece miss its loan payments and default, many fear that this would set off a chain of events that could lead to a messy Greek exit from the euro.
The deadlock has also alarmed the Obama administration in the United States, which has repeatedly urged all sides to reach a compromise.
Leaders of the Group of Seven summit are expected to also discuss the Greek issue during a meeting in Bavaria over the weekend.